DESCRIPTION (applicant's abstract): An understanding of the cellular processes that influence sexual differentiation of the brain during the perinatal period is important as they have enduring consequences on the normal behavior and physiology of an animal. Exposure to gonadal hormones during the perinatal period can either masculinize or feminize the brain. As gonadal hormones affect brain development by binding to intracellular steroid receptors located within the brain, it is important to understand how steroid hormones interact with steroid receptors to influence genomic activity and ultimately brain development. Recent studies have reported that steroid receptors interact with other proteins that are necessary for gene transcription. One such protein, called steroid receptor coactivator-1 (SRC-1), is known to be obligatory for steroid action in in vitro preparations however, it is not known if SRC-1 is required for steroid action within the brain. In the present series of experiments, we will determine if SRC-1 expression is sexually dimorphic within the brain during development and determine if SRC-1 protein is required for steroid action within the brain.